Induction of Melatonin Treatment on the Priming Resistance in Postharvest Plum Fruit

This study aimed to research the effectiveness and mode of the disease resistance induced by melatonin (MT) treatment in postharvest plum fruit. Plum fruit Cv ‘Fenghuang’ were treated with 10 mmol/L MT and/or inoculated with R. stolonifer, then stored for 5 days (20 ℃). Disease development, the contents of H₂O₂, total phenol and lignin and the activities of resistance-related enzyme were determined during the storage. The results showed that 10 mmol/L treatment effectively lowered the disease incidence and delayed the increase of lesion diameter of Rhizopus rot caused by R. stolonifer in plums. Single MT treatment could induce the activities of phenylpropanoid metabolic enzymes and the contents of total phenol and lignin in plums. MT treatment combined with R. tolonifer inoculation showed most significantly effects on the induction of H₂O₂ burst, and the activities of disease-resistance related enzymes such as chitinase, β-1,3-glucanase, phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumaric acid coenzyme A ligase (4-CL), peroxidase (POD) and polyphenol oxidase (PPO) as well as contents of total phenol and lignin in the samples during the storage. These results suggested that the MT treatment could activate the strong and rapid disease resistance upon the pathogenic infection by an induction of priming defence, by which the treatment resultantly maintained the overall quality in plums during the postharvest storage.